This application claims the priority of 196 19 641.8, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for preventing a vehicle from being parked with an activated roll-away preventer and unactivated parking brake. The method is based on the principle whereby the vehicle is held in the stationary state even after the end of activation of the service brake by applying a brake pressure.
As described in DE 36 21 076 A, the vehicle is held in the stationary state by virtue of the fact that valves are closed, then preventing the wheel brake cylinders from venting into the brake-fluid reservoir vessel. To this end, the valves are controlled by a control unit. The control unit evaluates input signals to determine whether the driver desires to drive the vehicle or whether a further stationary state of the vehicle is desired. This evaluation is based upon the input signals fulfilling prescribed triggering criteria. A device which carries out such a method is referred to as a roll-away preventer.
To the same effect, U.S. Pat. No. 4,787,205 discloses that a brake pressure, which maintains the stationary state of the vehicle, can be applied by the driver to the wheel brake cylinders independently of the activation of the brake pedal by generating or maintaining, a pressure difference between the chambers of a brake booster or an auxiliary booster corresponding thereto.
A disadvantage of maintaining the brake pressure in the known manner is that the vehicle is held in the stationary state without a deliberate decision by the driver. If the driver now wishes to park the vehicle, i.e. shut off the drive engine and leave the vehicle, there is the risk of the driver not activating the parking brake of the vehicle, because the at least temporarily maintained brake pressure keeps the vehicle in the stationary state even without the parking brake being activated. In order to ensure that the parking brake is nevertheless activated, the aforementioned DE 36 21 076 A1 proposes a warning buzzer which reminds the driver to activate the parking brake when the roll-away preventer is activated. In addition, the power supply of the valves which maintain the brake pressure is proposed to be independent of the position of the ignition key, so that, even when the ignition is switched off, these valves are held in the closed state.
Even these measures have disadvantages, however, for example, the warning buzzer may be disregarded because the driver expects to park for only a brief, insignificant, time. If the parking duration becomes unexpectedly prolonged, the driver is no longer aware of the poorly secured state of the vehicle which may result in increased risk. In addition, the vehicle battery may be discharged as a result of the valves being closed for a long time, in particular when the batteries have a poor charge state. Therefore, despite these measures, the parked vehicle may roll away. Also, as a result of leakages or gradual reduction of the pressure difference between the chambers of the brake booster, when the roll-away preventer is activated for a long time the applied brake pressure may no longer reliably prevent the vehicle from rolling.
An object of the present invention is to prevent unintentional rolling of a vehicle equipped with a roll-away preventer which, as a result of system failure, permits a pressure drop in the activated roll-away preventer.
This object has been achieved in accordance with the present invention in a situation which, if a brake pressure which prevents the motor vehicle from rolling in wheel brake cylinders, and the parking brake is not activated, the method prevents deactivation of the drive engine by the ignition key, or if a brake pressure which prevents the motor vehicle from rolling is applied in the wheel brake cylinders and the parking brake is not activated, the method preventing the ignition key from being withdrawn by a blocking mechanism.
Alternatively, the method involves generating brake pressure which prevents the rolling, by the steps of generating a pressure difference between the chambers of a brake booster, and controlling the pressure difference by a brake booster valve configured to be switchable by the control device. Thereby, when duration of the period over which a brake pressure is applied exceeds a specific measure, the valve is activated and a maximum pressure difference between the chambers of the brake booster is built up to damage the valve to remain permanently in a preselected position.
The methods according to the basic concept of the present invention ensure that the vehicle is not parked with an activated roll-away preventer and unactivated parking brake.
According to one embodiment of the present invention, the drive engine is prevented from being deactivated. An advantage of this approach is that as a result of the operation of the vehicle engine an energy source is continuously available. As a result, it is ensured, for example in underpressure brake boosters, that the engine-side chamber is supplied with underpressure (intake manifold pressure) while the pedal-side chamber can be supplied with atmospheric pressure by activating a switching valve. With overpressure brake systems or overpressure brake boosters, pressure can be continuously generated during operation via the compressor which is driven by the vehicle engine. If the brake pressure which prevents the vehicle from rolling is applied by activating valves assigned to the wheel brakes, there is always sufficient current available for valve activation while the vehicle engine is operating. Thus, the operation of the drive engine provides a high degree of protection against failure. Moreover, the driver will not park his vehicle as long as its drive engine is operating.
According to the present invention, the deactivation of the drive engine with an activated roll-away preventer and non-activated parking brake is prevented by virtue of the fact that a blocking mechanism prevents the key from being activated beyond a specific position. The key is initially in the operating position of the drive engine. A blocking mechanism then prevents the ignition key from being activated into a position (radio position or key withdrawal position) in which the drive engine of the vehicle is switched off.
According to another embodiment, the key is not prevented from being activated, but rather the activation function, namely the deactivation of the drive engine, is suppressed and the engine continues to operate. It is also contemplated that, in addition, a blocking mechanism prevents the key from being withdrawn from the ignition lock.
According to yet another embodiment, the deactivation of the vehicle is prevented by not allowing the key to be withdrawn from the ignition lock by way of a blocking mechanism for as long as the roll-away preventer is activated and the parking brake is not activated. Because a driver does not customarily leave the vehicle as long as the ignition key has not been withdrawn from the ignition, lock, this blocking mechanism prevents the driver from leaving the vehicle when it is in a state not reliably protected against rolling away.
According to still another embodiment, a previously mentioned procedure is particularly advantageous if the brake pressure preventing the rolling of the vehicle is applied and generates a pressure difference between the chambers of a brake booster. In conventional brake boosters, this pressure difference decreases gradually when the vehicle engine is switched off, creating a particularly large risk for the vehicle if it is parked without the parking brake being activated. Such risk is avoided with the present invention.
According to another aspect of the present invention, a roll-away preventer applies the brake pressure which prevents the vehicle from rolling by a pressure difference generated between the chambers of a brake booster independently of the activation of the brake pedal by the driver by a brake booster valve which can be switched by the control device, after a specific activation period has been exceeded, in the position which corresponds to an application of a maximum brake pressure. Then the valve is damaged to such an extent that it remains in this maximum brake pressure application position and therefore assumes this position permanently even without the valve being actuated.